Program POUs in PLCnext Engineer

This topic contains the following sections:

General information on program POUs

A program POU usually contains a logical combination of function/function block calls. Programs have an internal memory. Programs cannot be called from other POUs. A program must be instantiated in a task in order to be executed. Programs that are not instantiated in any task are not executed when running the controller application.

To add a program POU, right-click the folder 'COMPONENTS | Programming > Local > Programs' (or any subfolder) and select the context-menu command 'Add Program'.

The only safety-related program that can be executed by the Safety PLC is the 'S_Main' program (see following section "Program instances") which is marked by the safety overlay icon:
. It is, however, possible to add further safety-related program POUs while you are logged on to the Safety-related Area. Note that any other program than S_Main will not be executed.

Program instances

A program is only executed if it is instantiated. The instantiation of a non-safety-related program must be done by assigning it to a task in the 'Tasks and Events' editor. To open the 'Tasks and Events' editor, double-click the 'PLCnext' node in the PLANT.

The step-by-step procedures for creating IEC program instances in a task are described in the topic "Creating a program instance by assigning a program to a task".
The steps to instantiate an externally developed program are described in the topic "Integrating non-IEC 61131-3 programs into the PLCnext Technology task scheduling".

For the Safety PLC, the safety program instance S_Main is predefined and unchangeable: The Safety PLC executes exactly one task in which exactly one program is instantiated. Both the safety-related task and the program instance are created automatically on insertion of a controller with a Safety PLC in the PLANT. The program instance can neither be deleted nor edited and only a few properties of the task can be modified. Refer to the topic "Safety PLC Runtime Configuration" for details.

Further Info
The illustration in the topic "Instantiation: Program and FB Instances" explains the relation between types and instances and shows where instances of these types are possible.

Namespaces for program POUs

PLCnext Engineer supports namespaces for standard program POUs (not supported for safety-related program POUs). Namespaces allow you to organize and group POUs to make them unique within the project. They help you to ensure that the POU names do not collide with other names within the PLCnext Engineer project.

Refer to the help topic "Defining Namespaces for POUs" for details.